Erosion resistant hard composite materials

ABSTRACT

A hard composite composition may comprise a binder and a polymodal blend of matrix powder. The polymodal blend of matrix powder may have at least one first local maxima at a particle size of about 0.5 nm to about 30 μm, at least one second local maxima at a particle size of about 200 μm to about 10 mm, and at least one local minima between a particle size of about 30 μm to about 200 μm that has a value that is less than the first local maxima.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority as a divisional of U.S. patentapplication Ser. No. 13/336,842 which claims priority as acontinuation-in-part to U.S. patent application Ser. No. 12/902,433filed on Oct. 12, 2010 which claims priority as a continuation ofInternational Application Number PCT/US10/40065 filed on Jun. 25, 2010.

BACKGROUND

The present invention relates to a matrix powder composition for usealong with a binder to form a hard composite material. Moreparticularly, the invention pertains to a matrix powder composition foruse along with a binder to form a hard composite material wherein thehard composite material exhibits improved erosion resistance whileretaining strength. The matrix powder compositions of the presentinvention may be useful for tools that are involved in any applicationor operation in which a tool may be subjected to erosive and/or abrasiveconditions. Examples include subterranean applications that involve theuse of drill bits for drilling a well bore.

Hard composite materials have been formed by incorporating one or moreparticulate elements within a matrix powder, and then infiltrating thematrix powder with a binder metal to form a composite material with theparticulate elements incorporated within. This composite material can beuseful in tools or other devices that are subject to erosion. Compositematerials may include diamond composites material that can comprise asuitable binder with one or more discrete diamond-based particulateelements held therein. Additional particulate elements that have beenused include tungsten carbide. Tungsten carbide can be used in variousforms including, but not limited to, macrocrystalline tungsten carbideand cast tungsten carbide.

Hard composite materials have been used for a variety of purposes,including the manufacturing of earth-boring drill bits to provide someerosion resistance and improve mechanical strength. For example,polycrystalline diamond compact (“PDC”) cutters are known in the art foruse in earth-boring drill bits. Typically, drill bits using PDC cuttersinclude an integral bit body, which may substantially incorporate a hardcomposite. A plurality of PDC cutters can be mounted along the exteriorface of the bit body in extensions of the bit body called “blades.” EachPDC cutter has a portion which typically is brazed in a recess or pocketformed in the blade on the exterior face of the bit body. The PDCcutters are positioned along the leading edges of the bit body blades sothat as the bit body is rotated, the PDC cutters engage and drill theearth formation. In use, high forces may be exerted on the PDC cutters,particularly in the forward-to-rear direction. Additionally, the bit andthe PDC cutters may be subjected to substantial abrasive and erosiveforces.

While steel body bits may have toughness and ductility properties thatmake them resistant to cracking and failure due to impact forcesgenerated during drilling, steel may be, under certain condition, moresusceptible to erosive wear caused by high-velocity drilling fluids andformation fluids that carry abrasive particles, such as sand, rockcuttings, and the like. Generally, steel body bits often may be coatedwith a more erosion-resistant material, such as tungsten carbide, toimprove their erosion resistance. However, tungsten carbide and othererosion-resistant materials are relatively brittle relative to steel.During use, a thin coating of the erosion-resistant material may crack,peel-off or wear, exposing the softer steel body which may then berapidly eroded. This erosion can lead to loss of cutters as the areaaround the cutter is eroded away, causing the bit to fail.

Hardfacing is another example where hard composite materials have beenused. Hardfacing of metal surfaces and substrates is a technique tominimize or prevent erosion and abrasion of the metal surface orsubstrate. Hardfacing can be generally defined as applying a layer orlayers of hard, abrasion resistant material to a less resistant surfaceor substrate by plating, welding, spraying or other well knowndeposition techniques. Hardfacing can be used to extend the service lifeof drill bits and other downhole tools. Tungsten carbide and its variousforms are some of the more widely used hardfacing materials to protectdrill bits and other downhole tools associated with drilling andproducing oil and gas wells.

Rotary cone drill bits are often used for drilling boreholes for theexploration and production of oil and gas. This type of bit typicallyemploys three rolling cone cutters, also known as rotary cone cutters,rotatably mounted on spindles extending from support arms of the bit.The cutters are mounted on respective spindles that typically extenddownwardly and inwardly with respect to the bit axis so that the conicalsides of the cutters tend to roll on the bottom of a borehole andcontact the formation. For some applications, milled teeth are formed onthe cutters to cut and gouge in those areas that engage the bottom andperipheral wall of the borehole during the drilling operation. Theservice life of milled teeth may be improved by the addition of tungstencarbide particles to hard metal deposits on selected wear areas of themilled teeth by hardfacing.

Current composite materials can suffer from mass or material loss whensubject to an abrasive and/or erosive environment. This mass or materialloss can lead to tool failure or limited service life of the tool,possibly resulting in non-productive time (NPT). NPT is undesirable.Reducing NPT through extended service life of the tool would beadvantageous. As such, it would be desirable to provide an improved hardcomposite material having improved properties that include impactstrength, transverse rupture strength, hardness, abrasion resistance,and erosion resistance.

SUMMARY OF THE INVENTION

The present invention relates to a matrix powder composition for usealong with a binder to form a hard composite material. Moreparticularly, the invention pertains to a matrix powder composition foruse along with a binder to form a hard composite material wherein thehard composite material exhibits improved erosion resistance whileretaining strength.

Some embodiments of the present invention provide for a hard compositecomposition comprising: a binder and a polymodal blend of matrix powder.The polymodal blend of matrix powder has at least one first local maximaat a particle size of about 0.5 nm to about 30 μm, at least one secondlocal maxima at a particle size of about 200 μm to about 10 mm, and atleast one local minima between a particle size of about 30 μm to about200 μm that has a value that is less than the first local maxima.

Some embodiments of the present invention provide for a hard compositecomposition comprising: a binder and a polymodal blend of matrix powder.The polymodal blend of matrix powder has at least two particles with afirst particle having an aspect ratio of about 5 or greater.

Some embodiments of the present invention provide for a drill bitcomprising: a bit body and at least one cutting element for engaging aformation with at least a portion of the bit body comprising a hardcomposite material that comprises a binder and a polymodal blend ofmatrix powder. The polymodal blend of matrix powder has at least onefirst local maxima at a particle size of about 0.5 nm to about 30 μm, atleast one second local maxima at a particle size of about 200 μm toabout 10 mm, and at least one local minima between a particle size ofabout 30 μm to about 200 μm that has a value that is less than the firstlocal maxima.

Some embodiments of the present invention provide for a methodcomprising: providing a drill bit having at least one cutting elementfor engaging a formation and drilling a well bore in a subterraneanformation with the drill bit. The bit body comprises a binder and apolymodal blend of matrix powder. The polymodal blend of matrix powderhas at least one first local maxima at a particle size of about 0.5 nmto about 30 μm, at least one second local maxima at a particle size ofabout 200 μm to about 10 mm, and at least one local minima between aparticle size of about 30 μm to about 200 μm that has a value that isless than the first local maxima.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Figures are included to illustrate certain aspects of thepresent invention, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, as willoccur to those skilled in the art and having the benefit of thisdisclosure.

FIG. 1 is a particle size distribution plot showing a particle sizedistribution for an embodiment of a polymodal blend of matrix powder.

FIG. 2 is a schematic drawing showing an isometric view of an embodimentof a fixed cutter drill bit having a hard composite material bit bodyformed in accordance with the teachings of the present disclosure.

FIG. 3 is a schematic drawing in section elevation showing an embodimentof a drill bit formed in accordance with the teachings of the presentinvention at a downhole location in a well bore.

DETAILED DESCRIPTION

The present invention relates to a matrix powder composition for usealong with a binder to form a hard composite material. Moreparticularly, the invention pertains to a matrix powder composition foruse along with a binder to form a hard composite material wherein thehard composite material exhibits improved erosion resistance whileretaining strength. The matrix powder compositions of the presentinvention may be useful for tools that are involved in any applicationor operation in which a tool may be subjected to erosive and/or abrasiveconditions. Examples include subterranean applications that involve theuse of drill bits for drilling a well bore.

While many advantages of the present invention exist, only a few arediscussed herein. Without intending to be limited by theory, for hardcomposite materials, there is generally a tradeoff between improving theerosion resistance of a material and improving and/or maintaining itsmechanical strength. In general, additives added to the compositematerials to improve the erosion resistance tend to cause the materialto become brittle with a corresponding decrease in the mechanicalstrength. Conversely, additives used to improve the mechanical strengthtend to reduce the erosion resistance of the material. Striking theappropriate balance can be difficult.

The hard composite materials of the present invention provide botherosion resistance and mechanical strength at desirable levels. Forexample, in an embodiment of the present invention, a hard compositematerial comprising a polymodal blend of matrix powder and a binder mayimprove the erosion resistance of the material while improving and/ormaintaining its mechanical strength at desirable levels. As used herein,“maintaining mechanical strength” may depend on the particularapplication of the composite material and the specifications attendantthereto. Generally, it refers to the composite material being in linewith the minimum required mechanical strength specifications. Thepolymodal blend of matrix powder enables the realization of both erosionresistance and mechanical strength due, at least in part, to thepolymodal particle size distribution. Thus, the resulting hard compositematerial may be able to better withstand abrasion, wear, erosion andother stresses associated with repeated use in an abrasive and/orerosive environment.

Also disclosed are components produced using the hard compositematerials. For example, drill bits and hardfacing materials comprisingthe hard composite materials can be used to improve the erosionresistance of various components used in a subterranean environment. Insome embodiments, a drill bit may be formed from a hard compositematerial according to the present invention or a layer of hardfacingprepared from a hard composite material may be deposited on selectedexterior surfaces of a drill bit. Both of these applications may extendthe service life of the drill bit during downhole drilling.

In an embodiment, a hard composite material composition according to thepresent invention comprises a binder, and a polymodal blend of matrixpowder. The polymodal aspects of the blend described herein are relativeto a final blend of the matrix powder.

The following is understood in the context of a particle sizedistribution plot (e.g., particle size vs. vol % channel). One skilledin the art with the benefit of this disclosure should recognize theplurality of techniques available to achieve particle size measurementand in turn a particle size distribution plot (or the like). Suitabletechniques may include, but are not limited to, particle size analysiswith apparatuses like the “S3500 Particle Size Analyzer” available fromMicroTrac Inc. (2008) in Montgomeryville, Pa. and for smaller sizes the“NanoTrac” available from the same manufacturer, microscopy (e.g.,transmission electron microscopy, scanning electron microscopy, atomicforce microscopy, and optical microscopy), and the like. FIG. 1 is anexample of such a plot.

As used herein, a “polymodal” blend of matrix powder refers to matrixpowder with two or more different modes. As used herein, “modes” refersto a local maxima on a particle size distribution plot. The term “localmaxima” as used herein refers to a value at which the slope of the curveis about zero where the line transitions from a positive slope to anegative slope in the direction of increasing particle size.

In some embodiments, the polymodal blend of matrix powder may have atleast one local maxima at a particle size of about 30 μm or less(alternatively about 20 μm or less, about 10 μm or less, about 5 μm orless, about 1 μm or less, about 500 nm or less, or about 100 nm or less)as measured by techniques known to one skilled in the art. In someembodiments, the polymodal blend of matrix powder may have at least onelocal maxima at a particle size ranging from an upper limit of about 30μm (alternatively about 20 μm, about 10 μm, about 5 μm, about 1 μm,about 500 nm, or about 100 nm) to a lower limit of about 0.5 nm(alternatively about 1 nm, about 10 nm, about 100 nm, about 250 nm,about 500 nm, about 1 μm, or about 5 μm) as measured by techniques knownto one skilled in the art, where the at least one local maxima may rangefrom any lower limit to any upper limit, including ranges encompassedtherein, where the upper limit is chosen to be greater than the lowerlimit.

In some embodiments, the polymodal blend of matrix powder has at leastone local maxima at a particle size of about 200 μm or more(alternatively about 250 μm or more, about 300 μm or more, or about 400μm or more) as measured by techniques known to one skilled in the art.In some embodiments, the polymodal blend of matrix powder may have atleast one local maxima at a particle size ranging from a lower limit ofabout 200 μm (alternatively about 250 μm, about 300 μm, about 400 μm, orabout 1 mm) to an upper limit of about 10 mm (alternatively about 5 mm,about 1 mm, or about 500 μm) as measured by techniques known to oneskilled in the art, where the at least one local maxima may range fromany lower limit to any upper limit, including ranges encompassedtherein, where the upper limit is chosen to be greater than the lowerlimit. One skilled in the art with the benefit of this disclosure shouldunderstand that particles of larger size may be referred to as “pellets”and the like.

In some embodiments, the polymodal blend of matrix powder also may haveat least one local minima between a particle size of about 30 μm(alternatively about 20 μm, about 10 μm, about 5 μm, about 1 μm, about500 nm, or about 100 nm) to about 200 μm (alternatively about 250 μm,about 300 μm, about 400 μm, or 1 mm) that has a value that is less thanthe local maxima at a particle size of 30 μm or less (about 20 μm orless, about 10 μm or less, about 5 μm or less, about 1 μm, about 500 nm,or about 100 nm). The term “local minima” as used herein refers to avalue at which the slope of the curve is about zero where the linetransitions from a negative slope to a positive slope in the directionof increasing particle size. The local maxima and local minima can beone or more points on a plot that has zero slope; if a single point, theslope may be considered undefined by some, but for purposes of thisdisclosure, that single point is considered to have a zero slope.

FIG. 1 illustrates a particle size distribution of an example of a hardcomposite material composition of the present invention comprising apolymodal blend of matrix powder. FIG. 1 is an example of a plot from aS3500 Particle Size Analyzer available from MictroTrac, which is used todescribe the polymodal blend of matrix powder and compositions of thepresent invention. Shown at 102 is an example of a first local maxima.Shown at 104 is an example of a second local maxima. Comparatively shownat 106 is an example of a local minima that is less than local maxima102.

The polymodal blend of matrix powder useful with the present inventiongenerally lends erosion resistance to the hard composite material alongwith a high resistance to abrasion, erosion and wear. The polymodalblend of matrix powder can comprise particles of any erosion resistantmaterials which can be bonded (e.g., mechanically) with a binder to forma hard composite material. Suitable materials may include, but are notlimited to, carbides, nitrides, natural and/or synthetic diamonds, andany combination thereof.

In some embodiments, a matrix powder may comprise tungsten carbide (WC).Various types of tungsten carbide may be used with the presentinvention, including, but not limited to, stoichiometric tungstencarbide particles, cemented tungsten carbide particles, and/or casttungsten carbide particles. The first type of tungsten carbide,stoichiometric tungsten carbide, may include macrocrystalline tungstencarbide and/or carburized tungsten carbide. Macrocrystalline tungstencarbide is essentially stoichiometric WC in the form of single crystals,but some multicrystals of WC may form in larger particles. In someembodiments, macrocrystalline tungsten carbide may comprise additions ofcast carbide, Ni, Fe, Carbonyl of Fe, Ni, etc. Macrocrystalline tungstencarbide may also have characteristics such as hardness, wettability andresponse to contaminated hot, liquid binders which are different fromcemented carbides or spherical carbides. Methods of manufacturingmacrocrystalline tungsten carbide are known to those of ordinary skillin the art.

Carburized tungsten carbide, as known in the art, is a product of thesolid-state diffusion of carbon into tungsten metal at high temperaturesin a protective atmosphere. Carburized tungsten carbide grains aretypically multi-crystalline (e.g., they are composed of WCagglomerates). The agglomerates may form grains that are larger thanindividual WC crystals. Typical carburized tungsten carbide may containa minimum of 99.8% by weight of carbon infiltrated WC, with a totalcarbon content in the range of about 6.08% to about 6.18% by weight.

The second type of tungsten carbide, cemented tungsten carbide, mayinclude sintered spherical tungsten carbide and/or crushed cementedtungsten carbide. The terms “cemented carbide” and “cemented carbides”may be used within this application to include WC, MoC, TiC, TaC, NbC,Cr₃C₂, VC and solid solutions of mixed carbides such as WC—TiC,WC—TiC—TaC, WC—TiC—(Ta,Nb)C in a particulate binder (matrix) phase. Thebinder materials used to form cemented carbides may sometimes bereferred to as “bonding materials” in this patent application to helpdistinguish between binder materials used to form cemented carbides andbinder materials used to form a hard composite material and toolsincorporating the hard composite materials. Cemented carbides maysometimes be referred to as “composite” carbides or sintered carbides.Sintered tungsten carbide is commercially available in at least twobasic forms: crushed and spherical (or pelletized). Crushed sinteredtungsten carbide may be produced by crushing sintered components intofiner particles, resulting in more irregular and angular shapes, whereaspelletized sintered tungsten carbide may be generally rounded orspherical in shape. The particulate bonding material provides ductilityand toughness which often results in greater resistance to fracture(toughness) of cemented carbide pellets, spheres or other configurationsas compared to cast carbides, macrocrystalline tungsten carbide and/orformulates thereof.

A typical process for making cemented tungsten carbide generallyincludes providing a tungsten carbide powder having a predetermined size(or within a selected size range), and mixing the powder with a suitablequantity of cobalt, nickel, or other suitable bonding material. Themixture is typically prepared for sintering by either of two techniques:it may be pressed into solid bodies often referred to as green compacts,or alternatively, the mixture may be formed into granules or pelletssuch as by pressing through a screen, or tumbling and then screened toobtain more or less uniform pellet size. Such green compacts or pelletsare then heated in a controlled atmosphere furnace to a temperature nearthe melting point of cobalt (or the like) to cause the tungsten carbideparticles to be bonded together by the metallic phase. Sinteringglobules of tungsten carbide specifically yields spherical sinteredtungsten carbide. Crushed cemented tungsten carbide may further beformed from the compact bodies or by crushing sintered pellets or byforming irregular shaped solid bodies. The particle size, morphology,and quality of the sintered tungsten carbide can be tailored by varyingthe initial particle size of tungsten carbide and cobalt, controllingthe pellet size, adjusting the sintering time and temperature, and/orrepeated crushing larger cemented carbides into smaller pieces until adesired size is obtained.

The third type of tungsten carbide, cast tungsten carbide, may includespherical cast tungsten carbide and/or crushed cast tungsten carbide.Cast tungsten carbide has approximately the eutectic composition betweenbitungsten carbide, W₂C, and monotungsten carbide, WC. Cast carbide istypically made by heating tungsten in contact with carbon. Processes forproducing spherical cast carbide particles are known to those ofordinary skill in the art. For example, tungsten may be heated in agraphite crucible having a hole through which a resultant eutecticmixture of W₂C and WC may drip. This liquid may be quenched in a bath ofoil and may be subsequently crushed to a desired particle size to formwhat is referred to as crushed cast tungsten carbide. Alternatively, amixture of tungsten and carbon is heated above its melting point into aconstantly flowing stream which is poured onto a rotating coolingsurface, typically a water-cooled casting cone, pipe, or concaveturntable. The molten stream is rapidly cooled on the rotating surfaceand forms spherical particles of eutectic tungsten carbide, which arereferred to as spherical cast tungsten carbide.

Additional materials useful as matrix powder or as part of a matrixpowder blend include, but are not limited to, silicon nitride (Si₃N₄),silicon carbide (SiC), boron carbide (B₄C), cubic boron nitride (CBN),predominantly carbon structures (e.g., carbon fibers, carbon nanotubeswith any number of walls, fullerenes, graphite, and graphene includingfew layer graphene), iron oxide (e.g., Fe₂O₃, Fe₃O₄, FeO, variouscrystal structures thereof, and mixtures thereof), spherical carbides,low alloy sintered materials, cast carbides, silicon carbides, ironcarbides, macrocrystalline tungsten carbides, cast tungsten carbides,crushed sintered tungsten carbides, carburized tungsten carbides,steels, stainless steels, austenitic steels, ferritic steels,martensitic steels, precipitation-hardening steels, duplex stainlesssteels, iron alloys, nickel alloys, chromium alloys, HASTELLOYS®(nickel-chromium containing alloys, available from HaynesInternational), INCONELS® (austenitic nickel-chromium containingsuperalloys, available from Special Metals Corporation), WASPALOYS®(austenitic nickel-based superalloys, RENE® alloys (nickel-chromecontaining alloys, available from Altemp Alloys, Inc.), HAYNES® alloys(nickel-chromium containing superalloys, available from HaynesInternational), INCOLOYS® (iron-nickel containing superalloys, availablefrom Mega Mex), MP98T® (a nickel-copper-chromium superalloy, availablefrom SPS Technologies), TMS alloys, CMSX® alloys (nickel-basedsuperalloys, available from C-M Group), N-155 alloys, any mixturethereof, or any combination thereof. In some embodiments, particles ofthe matrix powders may be coated. By way of nonlimiting example,particles of the matrix powders may comprise diamond coated withtitanium. For purposes of the present application, the term cubic boronnitride refers to an internal crystal structure of boron atoms andnitrogen atoms in which the equivalent lattice points are at the cornerof each cell. Boron nitride particles typically have a diameter ofapproximately one micron and appear as a white powder. Boron nitride,when initially formed, has a generally graphite-like, hexagonal platestructure. When compressed at high pressures (such as 10⁶ PSI) cubicboron nitride particles will be formed with a hardness very similar todiamonds. However, the mechanical strength of cubic boron nitride isgenerally low in comparison with many steel alloys.

The various materials useful as a matrix powder may be selected so as toprovide a polymodal blend of matrix powder and final hard compositematerial that is tailored for a particular application. For example, thetype, shape, and/or size of a particulate material used in the formationof a hard composite material may affect the material properties of thematerial, including, for example, fracture toughness, transverse rupturestrength, and erosion resistance. Suitable shapes of particulates mayinclude, but are not limited to, spherical and/or ovular, substantiallyspherical and/or ovular, discus and/or platelet, flake, ligamental,acicular, fibrous (such as high-aspect ratio shapes), polygonal (such ascubic), randomly shaped (such as the shape of crushed rocks), faceted(such as the shape of crystals), or any hybrid thereof. It should benoted that particles with aspect ratios may have at least one dimensionthat falls within the size distributions of the particles as describedherein (e.g., particles may be whiskers of tungsten carbide having adiameter ranging from about 1 μm to about 5 μm, thereby falling within arange described herein for the smaller particles). Without being limitedby theory, it is believed that particulates having aspect ratios mayadvantageously provide bridging and enhance crack resistance of articlesformed therefrom, especially those particles with aspect ratios of about5 or greater. In some embodiments, particulates may have an aspect ratioranging from a lower limit of about 1 (alternatively about 1.5, about 2,about 5, about 10, or about 50) to an upper limit of about 5000(alternatively about 1000, about 500, about 100, about 50, about 10, orabout 5), where the aspect ratio may range from any lower limit to anyupper limit, including ranges encompassed therein, where the upper limitis chosen to be greater than the lower limit. By way of nonlimitingexample, particles may include whiskers, rods, nanorods, wires,nanowires, lobal particles (e.g., tripods and tetrapods), nanostars(like nanotripods and nanotetrapods), nanospheres, and nanorices. By wayof another nonlimiting example, particles may include nanowires oftungsten carbide having an aspect ratio of about 10 to about 500.

In some embodiments, the polymodal blend of matrix powder may comprise asingle material or a blend of materials. In addition, two or more matrixpowders may be combined as necessary to form the polymodal blend ofmatrix powder with the characteristics described herein.

Without intending to be limited by theory, it is believed that thematrix powder with the larger particle size distribution may be at leastpartly responsible for the improved erosion resistance of a hardcomposite material formed using the polymodal blend of matrix powder.Similarly, the matrix powder with the smaller particle size distributionmay be at least partly responsible for maintaining the mechanicalproperties (e.g., fracture toughness, transverse rupture strength, etc.)of a hard composite material formed from the polymodal blend of matrixpowder, which may be further enhanced by homogeneous distribution of thesmaller particles, especially at smaller particle sizes (e.g., belowabout 10 μm or below about 1 μm).

The terms “binder” or “binder material” may be used in this applicationto include copper, cobalt, nickel, iron, zinc, manganese, any alloys ofthese elements, any combinations thereof, or any other materialsatisfactory for use in forming a hard composite material comprising thepolymodal blend of matrix powder described above. Such binders generallyprovide desired ductility, toughness and thermal conductivity for anassociated hard composite material. Binder materials may cooperate withthe particulate material(s) present in the matrix powders selected inaccordance with teachings of the present disclosure to form hardcomposite materials with increased erosion resistance as compared tomany conventional hard composite materials.

The hard composite materials of the present invention may be formedusing any technique known in the art. A typical formation process forcasting hard composite materials may begin by forming a mold in theshape of a desired component. Displacement materials such as, but notlimited to, mold inserts, and additives necessary to obtain the desiredshape may then be loaded into the mold assembly. The mold assembly maythen be loaded with the polymodal blend of matrix powder. As the moldassembly is being filled, a series of vibration cycles may be used toassist packing of the polymodal blend of matrix powder, as necessary.The vibrations may help ensure a consistent density of the matrixpowders within a desired range required to achieve the desiredcharacteristics for the hard composite material.

The binder material may then be placed on top of the mold assembly, andmay be optionally covered with a flux layer. A cover or lid may beplaced over the mold assembly as necessary. The mold assembly andmaterials disposed therein may be preheated and then placed in afurnace. When the furnace temperature reaches the melting point of thebinder material, the resulting liquid binder material may infiltrate thepolymodal blend of matrix powder. The mold assembly may then be cooledbelow the solidus temperature to form the hard composite material. Themold assembly may be removed to allow the hard composite material thatis the shape of a desired component to be removed for use. Use of thisprocedure may allow for a variety of components to be formed from thehard composite materials described herein.

In an embodiment, a hard composite material of the present invention maydisplay improved erosion resistance while maintaining or improving itsmechanical strength. The improved erosion resistance may be measured byan improvement in the volume loss (e.g., an improvement represents areduction in the volume loss and/or erosion rate) of a sample whensubjected to a Slurry Erosion Test procedure (a “SET” procedure), whichhas been developed to test the hard composite materials producedaccording to the present invention. While not intending to be limited bytheory, it is believed that the SET procedure, compared to other testprocedures currently available, allows a measurement of the erosionresistance of a material under conditions that more closely match thoseencountered in a subterranean formation during drilling or any othertreatment operation involving erosive conditions.

The SET procedure can be used to determine the erosion rate for a sampleof a material. First, a test specimen can be provided and the mass anddensity of the test specimen may be measured and recorded. A testingcontainer may be provided that is suitably sized to hold the testspecimen along with an erosion material. In an embodiment, a plasticcontainer with a volume from about 50 mL to about 2 L can be used as thetest container for small samples, though a larger container constructedof an appropriate material can be used for larger samples. The erosionmaterial can be any suitable abrasive material capable of eroding thetest specimen. In some embodiments, fine silica powder and/or aluminapowder may be used as the erosion material. The erosion material isplaced in the testing container, water may be added, and the containermay be agitated to thoroughly mix the erosion material and the water. Inan embodiment, a sufficient amount of water may be added to form aslurry and may typically comprise about 20% to about 99% of the volumeof the testing container. The ratio of erosion material to water may bevaried to model a specific density fluid, as desired (e.g., a drillingmud). One of ordinary skill in the art can determine the ratio oferosion material to water based on the desired density of fluid. Thetest specimen may be placed in the testing container and the testingcontainer may be sealed. The testing container may be loaded into adevice capable of moving the sample through the slurry within thetesting container. For example, a 3-dimensional blender/mixer as knownto one of ordinary skill in the art may be used. The mixer may bestarted and the beginning time may be recorded. The testing containermay then be agitated for a period of time. The time period selected maydepend on the test specimen size, the erosion material, and the testspecimen composition. In an embodiment, the time period may range fromabout 1 to about 72 hours. In general, the test results may be scalablebased on time. The mixer may then be stopped and the time recorded. Thetest specimen can be removed, rinsed, and dried prior to measuring andrecording the mass and density of the test specimen. The mass loss canbe calculated as the difference between the initial mass and the finalmass. The volume loss can be calculated based on the mass loss and theinitial and final densities. A volume loss percentage can be calculatedbased on the volume loss and the initial volume. An erosion rate canthen be determined on a mass or volume basis by dividing the mass lossor volume loss, respectively, by the test run time.

The test specimen can then be retested according to the same procedureoutlined above at least two more times. In a preferred embodiment, fresherosion material and water may be used for each test. Reusing theerosion material may result in skewed results due, at least in part, tothe wearing of the erosion material during the previous testingprocedures. But the erosion material may be reused in successive tests,if desired, as long as that variable is taken into account whenevaluating the results. Due to the geometric variations in the testsamples, the first run in the test procedure may show a higher volumeloss percentage than subsequent runs. The second and third runs may beaveraged, along with any additional runs, to determine the erosion rateand volume loss percentage for the test specimen.

In an embodiment, a “specific SET procedure” may be used to determinethe erosion rate on either a mass or volume basis according to thefollowing parameters. First, a test specimen of material with a mass ofbetween about 1 g and 50 g is provided and the mass and density of thetest specimen is measured and recorded. A 500 mL plastic test containeris provided, and a 100 g alumina powder sample is used as the erosionmaterial. The alumina powder is placed in the testing container, 375 gof water is added, and the container is agitated to thoroughly mix theerosion material and the water. The test specimen is placed in thetesting container and the testing container is sealed. The testingcontainer is loaded into a 3-dimensional blender/mixer (e.g., a “TurbulaShaker Mixer Type T2 F” available from Willy A. Bachofen AGMashinenfabrik of Switzerland, or equivalent) and set to a mixing speedof 34 min⁻¹, where the effective speed of the mixer depends on severalinfluences, and may not exactly correspond to the set speed. The mixeris started and the beginning time is recorded. The testing container isthen agitated for a period of about 24 hours. The mixer is stopped andthe time recorded. The test specimen is removed, rinsed, and dried priorto measuring and recording the mass and density of the test specimen.The mass loss can be calculated as the difference between the initialmass and the final mass. The volume loss can be calculated based on themass loss and the initial and final densities. A volume loss percentagecan be calculated based on the volume loss and the initial volume. Thetest procedure is then repeated at least 2 additional times using freshalumina powder and water for each run. The average values of the massloss and volume loss from the second and subsequent runs is then used todetermine erosion rate on a mass or volume basis by dividing the massloss or volume loss, respectively, by the test run time.

In an embodiment, a hard composite material produced according to thepresent invention may have an erosion rate of less than 0.06% vol/hr asdetermined by the specific SET procedure outlined above. In anotherembodiment, a hard composite material produced according to the presentinvention may have an erosion rate of less than 0.055% vol/hr, oralternatively less than 0.053% vol/hr as determined by the specific SETprocedure outlined above.

In an embodiment, the hard composite materials of the present inventionmay be used to form at least a portion of a rotary drill bit. Rotarydrill bits can be used to drill oil and gas wells, geothermal wells, andwater wells. Rotary drill bits may be generally classified as rotarycone or roller cone drill bits and fixed cutter drilling equipment ordrag bits. Fixed cutter drill bits or drag bits are often formed with amatrix bit body having cutting elements or inserts disposed at selectlocations of exterior portions of the matrix bit body. Fluid flowpassageways are typically formed in the matrix bit body to allowcommunication of drilling fluids from associated surface drillingequipment through a drill string or drill pipe attached to the matrixbit body. Such fixed cutter drill bits or drag bits may sometimes bereferred to as “matrix drill bits.” The terms “matrix drill bit” and“matrix drill bits” may be used in this application to refer to “rotarydrag bits,” “drag bits,” and/or “fixed cutter drill bits.”

FIG. 2 is a schematic drawing showing one example of a matrix drill bitor fixed cutter drill bit that may be formed with a hard compositematerial in accordance with teachings of the present disclosure. Forembodiments such as shown in FIG. 2, matrix drill bit 20 may includemetal shank 30 with hard composite material bit body 50 securelyattached thereto. Metal shank 30 may be described as having a generallyhollow, cylindrical configuration defined in part by a fluid flowpassageway therethrough. Various types of threaded connections, such asAmerican Petroleum Institute (API) connection or threaded pin 34, may beformed on metal shank 30 opposite from hard composite material bit body50.

In some embodiments, a generally cylindrical metal blank or castingblank may be attached to hollow, generally cylindrical metal shank 30using various techniques. For example annular weld groove 38 may beformed between adjacent portions of the blank and metal shank 30. Weld39 may be formed in groove 38 between the blank and shank 30. The fluidflow passageway or longitudinal bore preferably extends through metalshank 30 and the metal blank. The metal blank and metal shank 30 may beformed from various steel alloys or any other metal alloy associatedwith manufacturing rotary drill bits.

A matrix drill bit may include a plurality of cutting elements, inserts,cutter pockets, cutter blades, cutting structures, junk slots, and/orfluid flow paths that may be formed on or attached to exterior portionsof an associated bit body. For an embodiment such as shown in FIG. 2, aplurality of cutter blades 52 may form on the exterior of hard compositematerial bit body 50. Cutter blades 52 may be spaced from each other onthe exterior of hard composite material bit body 50 to form fluid flowpaths or junk slots therebetween.

A plurality of nozzle openings 54 may be formed in hard compositematerial bit body 50. Respective nozzles 56 may be disposed in eachnozzle opening 54. For some applications nozzles 56 may be described as“interchangeable” nozzles. Various types of drilling fluid may be pumpedfrom surface drilling equipment (not expressly shown) through a drillstring (not expressly shown) attached with threaded pin 34 and the fluidflow passageways to exit from one or more nozzles 56. The cuttings,downhole debris, formation fluids and/or drilling fluid may return tothe well surface through an annulus (not expressly shown) formed betweenexterior portions of the drill string and interior of an associated wellbore (not expressly shown).

A plurality of pockets or recesses may be formed in cutter blades 52 atselected locations. Respective cutting elements or inserts 60 may besecurely mounted in each pocket to engage and remove adjacent portionsof a downhole formation. Cutting elements 60 may scrape and gougeformation materials from the bottom and sides of a well bore duringrotation of matrix drill bit 20 by an attached drill string. In someembodiments, various types of polycrystalline diamond compact (PDC)cutters may be satisfactorily used as inserts 60. A matrix drill bithaving such PDC cutters may sometimes be referred to as a “PDC bit”.

U.S. Pat. No. 6,296,069 entitled Bladed Drill Bit with CentrallyDistributed Diamond Cutters and U.S. Pat. No. 6,302,224 entitledDrag-Bit Drilling with Multiaxial Tooth Inserts, both incorporatedherein in their entirety, show various examples of blades and/or cuttingelements which may be used with a composite matrix bit bodyincorporating teachings of the present disclosure. It will be readilyapparent to persons having ordinary skill in the art that a wide varietyof fixed cutter drill bits, drag bits and other drill bits may besatisfactorily formed with a hard composite material bit bodyincorporating teachings of the present disclosure. The presentdisclosure is not limited to hard composite matrix drill bit 20 or anyspecific features as shown in FIG. 2.

Matrix drill bits can be formed according to the present invention byplacing a polymodal blend of matrix powder into a mold and infiltratingthe hard composite material with a binder. The mold may be formed bymilling a block of material such as graphite to define a mold cavitywith features that correspond generally with desired exterior featuresof the resulting matrix drill bit. Various features of the resultingmatrix drill bit such as blades, cutter pockets, and/or fluid flowpassageways may be provided by shaping the mold cavity and/or bypositioning temporary displacement material within interior portions ofthe mold cavity. A preformed steel shank or bit blank may be placedwithin the mold cavity to provide reinforcement for the matrix bit bodyand to allow attachment of the resulting matrix drill bit with a drillstring. Once the quantity of the polymodal blend of matrix powder isplaced within the mold cavity, the mold may be infiltrated with a moltenbinder which can form a hard composite material bit body aftersolidification of the binder with the polymodal blend of matrix powder.

A matrix drill bit may be formed using the hard composite materials ofthe present invention that may have a functional gradient. In thisembodiment, one or more portions of the matrix drill bit (e.g., an outerlayer) may be formed using the polymodal blend of matrix powderdisclosed herein, while a different material composition can be used toform the remaining portions of the matrix drill bit (e.g., the interiorportions). As an example, a resulting matrix drill bit can be describedas having a “functional gradient” since the outer portions may haveimproved erosion resistance while the inner portions may exhibitimproved mechanical strength by having a different material composition.Methods of forming matrix drill bits with different functional zones isdescribed in U.S. Pat. No. 7,398,840 entitled Matrix Drill Bits andMethod of Manufacturing, which is incorporated herein in its entirety.

A tool comprising a hard composite material in whole or in part asformed in accordance with the teachings of the present invention may beused for other applications in a wide variety of industries and is notlimited to downhole tools for the oil and gas industry.

In an embodiment, the hard composite materials of the present inventionmay be used to form at least a portion of a rotary cone drill bit. FIG.3 is a schematic drawing showing one example of a rotary cone drill bitthat may be formed with a hard composite material in accordance withteachings of the present disclosure. For embodiments such as shown inFIG. 3, drill bit 80 includes a bit body 84 adapted to be connected atits pin or threaded connection 86 to the lower end of rotary drillstring 88. Threaded connection 86 and the corresponding threadedconnection of the drill string are designed to allow rotation of drillbit 80 in response to rotation of the drill string 88 at the wellsurface (not shown). Bit body 84 includes a passage (not shown) thatprovides downward communication for drilling mud or the like passingdownwardly through the drill string. The drilling mud exits throughnozzle 92 and is directed to the bottom of the borehole and then passesupward in the annulus between the wall of the borehole and the drillstring, carrying cuttings and drilling debris therewith. Depending frombit body 84 are three substantially identical arms 94. Only two arms 94are shown in FIG. 3. The lower end portion of each of the arms 94 isprovided with a bearing pin or spindle (not shown), to rotatably supportgenerally conical cutter cone assembly 82. On each cutter cone assembly82 are milled teeth capable of eroding the formation face when placed incontact with the formation.

The cutting action or drilling action of a rotary cone drill bit occursas the cutter cone assemblies are rolled around the bottom of theborehole by the rotation of an associated drill string. The cutter coneassemblies may be referred to as “rotary cone cutters” or “roller conecutters.” The inside diameter of the resulting borehole is generallyestablished by the combined outside diameter, or gage diameter, of thecutter cone assemblies. The cutter cone assemblies may be retained on aspindle by a conventional ball retaining system comprising a pluralityof ball bearings aligned in a ball race.

Rotary cone drill bits can be manufactured from a strong, ductile steelalloy, selected to have good strength, toughness and reasonablemachinability. Such steel alloys generally do not provide good, longterm cutting surfaces and cutting faces on the respective cutter coneassemblies because such steel alloys are often rapidly worn away duringdownhole drilling operations. To increase the downhole service life ofthe respective rotary cone drill bits, a hard composite material asdisclosed herein may be used to form at least a portion of the shirttailsurfaces, the backface surfaces, the milled teeth, and/or the insertsassociated with the rotary cone drill bits. Hard composite material mayalso be used to form any other portions of the rotary cone drill bitsthat are subjected to intense erosion, wear and abrasion during downholedrilling operations. For some applications, essentially all of theportions of the rotary cone drill bits with exposed, exterior surfacesmay be formed using a hard composite material of the present invention.For example, spindle surfaces 20 may be formed using a hard compositematerial according to the present invention.

In an embodiment, a desired component can be hardfaced using a hardcomposite material of the present invention to improve the wear anderosion resistance of the component. Hardfacing can be defined asapplying a layer or layers of hard, abrasion resistant materialcomprising a hard composite material as disclosed herein to a lessresistant surface or substrate by plating, welding, spraying or otherwell known deposition techniques. Hardfacing can be used to extend theservice life of drill bits and other downhole tools used in the oil andgas industry.

A hard composite material may be formed on and/or bonded to workingsurface of a substrate using various techniques associated withhardfacing. In some embodiments, the hard composite material may beapplied by welding techniques associated with conventional hardfacing.In an embodiment, the hard composite materials may be applied viawelding by first forming a welding rod or similar structure comprisingthe hard composite material and/or a hard composite material precursor(i.e., a mixture of the polymodal blend of matrix powder and a binder,which may be in particulate form). In an embodiment, a welding rod mayinclude a hollow tube which can be closed at both ends to contain a hardcomposite material comprising a polymodal blend of matrix powder, andoptionally, a binder in particulate form. In some embodiments, thehollow tube may comprise the binder material that, once melted, formsthe hard composite material with the polymodal blend of matrix powdercontained therein. Alternatively, the welding rod may comprise a solidrod of the hard composite material, and may optionally compriseadditional additives as described in more detail below. In anembodiment, the hard composite material may be included as part of acontinuous welding rod, composite welding rod, or welding rope.

In some embodiments, the welding rod may optionally comprise adeoxidizer and a temporary resin binder. Examples of deoxidizerssatisfactory for use with the present invention include various alloysof iron, manganese, and silicon. The welding rod may compriseadditional, optional materials such as powders of hard material selectedfrom the group consisting of tungsten, niobium, vanadium, molybdenum,silicon, titanium, tantalum, zirconium, chromium, yttrium, boron, carbonand carbides, nitrides, or oxides. The welding rod may also optionallyinclude a powdered mixture selected from the group consisting of copper,nickel, iron, cobalt and alloys of these elements to act as a binderwhen hardfacing a substrate. The specific compounds and elementsselected for inclusion in the welding rod may depend upon the intendedapplication for the resulting hard composite material the substrate, andthe selected welding technique.

During the welding process, the surface of a substrate may besufficiently heated to melt portions of the substrate and formmetallurgical bonds between the hard composite material and thesubstrate. In addition to oxyacetylene welding, atomic hydrogen weldingtechniques, tungsten inert gas (TIG-GTA), stick welding or SMAW and GMAWwelding techniques may be satisfactorily used to apply the hardcomposite material to a surface of a substrate.

In some embodiments, the hard composite material may be formed directlyon the surface of a substrate. In these embodiments, a mixture of thepolymodal blend of matrix powder and the binder in particulate form maybe blended with an organic resin and sprayed on a surface of asubstrate. A laser may then be used to densify and fuse the resultingpowdered mixture with the surface of the substrate to form the desiredmetallurgical bonds as previously discussed. Tube rod welding with anoxyacetylene torch may be satisfactorily used to form metallurgicalbonds between hard composite material and substrate and metallurgicalbonds between matrix portion and coating. For other applications, laserwelding techniques may be used to form hard composite material onsubstrate. Both tube rod welding techniques and laser welding techniquesare known to those of ordinary skill in the art.

For some less stringent applications, hard composite material may beformed on a substrate using plasma spray techniques and/or flame spraytechniques, which are both associated with various types of hardfacing.Plasma spray techniques typically form a mechanical bond between theresulting hard composite material in the hardfacing and the associatedsubstrate. Flame spraying techniques also typically form a mechanicalbond between the hard composite material in the hardfacing and thesubstrate. For some applications, a combination of flame spraying andplasma spraying techniques may also be used to form a metallurgical bondbetween the hard composite material and the substrate. In general,hardfacing techniques which produce a metallurgical bond are preferredover those hardfacing techniques which provide only a mechanical bondbetween the hard composite material and the substrate.

In an embodiment, forming a hardfacing comprising a hard compositematerial formed in accordance with the teachings of the presentinvention may be used on a wide variety of metallic bodies andsubstrates. For example, a hardfacing comprising a hard compositematerial may be placed on roller cone drill bits, fixed cutter drillbits, sleeve for drill bits, coring bits, underreamers, hole openers,stabilizers and shock absorber assemblies. A hardfacing comprising ahard composite material formed in accordance with the teachings of thepresent invention may be used on other tools in a wide variety ofindustries and is not limited to downhole tools for the oil and gasindustry.

Any suitable hardfacing techniques or methods can be used with the hardcomposite materials of the present invention. Additional suitablehardfacing techniques that can incorporate the hard composite materialof the present invention are described in U.S. Pat. No. 6,469,278entitled Hardfacing Having Coated Ceramic Particles or Coated Particlesof Other Hard Materials, which is incorporated herein in its entirety.

To determine if a device has incorporated a hard composite material ofthe present invention having a polymodal blend of matrix powder, certainimaging techniques may be suitable. An example of a suitable analysistechnique is available from Smart Imaging Technologies in Houston, Tex.The software involved as of the time of this invention is “SIMAGIS®.”Metallographic images of the infiltrated hard composite material may beuploaded into the SIMAGIS software. Contrasting techniques known in theart may be used, if needed. Metallographic images are analyzed by thesoftware to determine particle size distribution for components of thehard composite material that has been incorporated into the device. TheSIMAGIS presentation of data may vary from the data from the Microtracparticle size analyzer due to, among other things, channel width whichmay differ between the two techniques. The data from both techniques maybe correlated by one skilled in the art.

In an embodiment, a method comprises providing a drill bit comprising abit body formed from a hard composite material. The hard compositematerial generally comprises a binder, and a polymodal blend of matrixpowder. In some embodiments, the polymodal blend of matrix powder has alocal maxima at a particle size of 30 μm or less, a local maxima at aparticle size of 200 μm or more, and a local minima between a particlesize of about 30 μm to about 200 μm that has a value that is less thanthe local maxima at a particle size of 30 μm or less. The drill bit alsohas at least one cutting element for engaging a formation. The drill bitis then used to drill a well bore in a subterranean formation.

To facilitate a better understanding of the present invention, thefollowing examples of preferred embodiments are given. In no way shouldthe following examples be read to limit, or to define, the scope of theinvention.

Examples

A series of experiments were carried out according to the specific SETprocedure described above. First, a test specimen of material with amass of between about 2 g and 30 g was provided and the mass and densityof the test specimen was measured and recorded. The formulations of eachspecimen are shown below in Table 1. Test samples 1 through 4 wereformulated as provided by the manufacturer. Test samples 5 and 6 wereprepared according to the methods disclosed herein.

TABLE 1 Sample No. Composition 1 D63, available from Halliburton EnergyServices of Houston, TX 2 D63, available from Halliburton EnergyServices of Houston, TX 3 P90, available from Kennametal Inc. ofLatrobe, PA 4 P90, available from Kennametal Inc. of Latrobe, PA 5Polymodal blend of matrix powder Sample 1 6 Polymodal blend of matrixpowder Sample 2

The samples were tested using a 500 mL plastic test container, and 100 gof fine silica powder sample. The silica powder was placed in thetesting container, 375 g of water was added, and the container wasagitated to thoroughly mix the erosion material and the water. The testspecimen was placed in the testing container and the testing containerwas sealed. The testing container was loaded into a 3-dimensionalblender/mixer. The mixer was started and the beginning time wasrecorded. The testing container was then agitated for a period of time.The mixer was stopped and the time recorded. The test specimen wasremoved, rinsed, and dried prior to measuring and recording the mass anddensity of the test specimen. The mass loss was calculated as thedifference between the initial mass and the final mass. The volume losswas calculated based on the mass loss and the initial and finaldensities. A volume loss percentage was calculated based on the volumeloss and the initial volume. The test procedure was then repeated 3additional times using fresh silica powder and water for each run. Thevalues of the volume loss were then used to determine erosion rate on avolume basis by dividing the volume loss by the test run time. Theresults for each sample are presented below in Table 2.

TABLE 2 Test Run Volume Loss Per Hour (% of initial volume) Average ofruns Sample 1 2 3 4 2-4 (% vol. loss/hr) 1 0.063% 0.065% 0.061% 0.063%0.063% 2 0.063% 0.065% 0.061% 0.063% 0.063% 3 0.095% 0.094% 0.086%0.088% 0.089% 4 0.095% 0.094% 0.086% 0.088% 0.089% 5 0.061% 0.057%0.052% 0.053% 0.054% 6 0.058% 0.056% 0.052% 0.052% 0.053%

The results demonstrate to one of ordinary skill in the art that theformulations according to the present invention reduce the erosion rateas measured by the volume loss per time relative to comparative samples.Test samples 5 and 6 as prepared according to the teachings of thepresent disclosure show an erosion rate below those of the othercomparative samples.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

The invention claimed is:
 1. A drill bit comprising: a bit body; and atleast one cutting element for engaging a formation; wherein at least aportion of the bit body comprises a hard composite material comprising:a binder; a polymodal blend of matrix powder, wherein the polymodalblend of matrix powder is characterized by a particle size distributionhaving at least one first local maxima at a particle size of about 0.5nm to about 30 μm, at least one second local maxima at a particle sizeof about 200 μm to about 10 mm, and at least one local minima between aparticle size of about 30 μm to about 200 μm, wherein the local minimahas a volume percent value that is less than the first local maxima;wherein the polymodal blend of matrix powder comprises at least oneparticle having an aspect ratio of about 5 or greater selected from thegroup consisting of: a whisker, a rod, a nanorod, a wire, a nanowire, ananostar, and a nanorice.
 2. The drill bit of claim 1 wherein the drillbit is a fixed cutter drill bit.
 3. The drill bit of claim 1 wherein thedrill bit is a rotary cone drill bit.
 4. The drill bit of claim 1wherein the first local maxima is at a particle size of about 0.5 nm toabout 1 μm.
 5. The drill bit of claim 1 wherein the first local maximais at a particle size of about 1 μm to about 10 μm.
 6. The drill bit ofclaim 1 wherein the polymodal blend of matrix powder comprises at leastone material selected from the group consisting of: a carbide, anitride, a natural diamond, a synthetic diamond, predominantly carbonstructures, iron oxides, steels, stainless steels, austenitic steels,ferritic steels, martensitic steels, precipitation-hardening steels,duplex stainless steels, iron alloys, nickel alloys, chromium alloys,and any combination thereof.
 7. The drill bit of claim 1 wherein thepolymodal blend of matrix powder comprises at least one materialselected from the group consisting of: stoichiometric tungsten carbide,cemented tungsten carbide, cast tungsten carbide, and any combinationthereof.
 8. The drill bit of claim 1 wherein the polymodal blend ofmatrix powder comprises at least one material selected from the groupconsisting of: molybdenum carbide, titanium carbide, tantalum carbide,niobium carbide, chromium carbide, vanadium carbide, silicon carbide,boron carbide, solid solutions thereof, and any combination thereof. 9.The drill bit of claim 1 wherein the polymodal blend of matrix powdercomprises at least one material selected from the group consisting of:silicon nitride, cubic boron nitride, and any combination thereof. 10.The drill bit of claim 1 wherein the binder comprises at least onematerial selected from the group consisting of: copper, cobalt, nickel,iron, zinc, manganese, any alloys of these elements, and anycombinations thereof.
 11. The drill bit of claim 1 wherein the hardcomposite material has an erosion rate of less than 0.06% volume perhour based on a Specific Slurry Erosion Test Procedure comprisingeroding a test specimen of the hard composite material against anerosion material for a test run time; measuring a volume loss of thetest specimen; and calculating an erosion rate by dividing the volumeloss by the test run time.